111 research outputs found
Monthly 43 GHz VLBA Polarimetric Monitoring of 3C120 over 16 Epochs: Evidence for Trailing Shocks in a Relativistic Jet
We present a 16-month sequence of monthly polarimetric 43 GHz VLBA images of
the radio galaxy 3C 120. The images probe the inner regions of the radio jet of
this relatively nearby superluminal radio galaxy at a linear resolution of 0.07
pc ( km s Mpc). We follow the
motion of a number of features with apparent velocities between 4.010.08
and . A new superluminal knot, moving at , is observed to be ejected from the core at a time
coincident with the largest flare ever observed for this source at millimeter
wavelengths. Changes in the position angle of this component, as well as a
progressive rotation of its magnetic polarization vector, suggest the presence
of a twisted (resembling a helix in projection) configuration of the underlying
jet magnetic field and jet geometry. We identify several knots that appear in
the wake of the new superluminal component, moving at proper motions
times slower than any of the other moving knots observed in 3C 120. These
features have properties similar to those of the ``trailing'' shocks seen in
relativistic, time-dependent, hydrodynamical and emission simulations of
compact jets. Such trailing compressions are triggered by pinch-mode jet-body
instabilities caused by the propagation of a strong perturbation, which we
associate with the new strong superluminal component.Comment: 4 pages, 5 figures, accepted for publication in Astrophysical Journal
Letter
MAPCAT: Monitoring AGN with Polarimetry at the Calar Alto Telescopes
We introduce MAPCAT, a long-term observing program for "Monitoring of AGN
with Polarimetry at the Calar Alto Telescopes". Multi-spectral-range studies
are critical to understand some of the most relevant current problems of high
energy astrophysics of blazars such as their high energy emission mechanisms
and the location of their gamma-ray emission region through event associations
across the spectrum. Adding multi-spectral-range polarimetry allows for even
more reliable identification of polarized flares across the spectrum in these
kind of objects, as well as for more accurate modeling of their magnetic field.
As part of a major international effort to study the long term multi-spectral
range polarimetric behavior of blazars, MAPCAT uses -since mid 2007- CAFOS on
the 2.2m Telescope at the Calar Alto Observatory (Almeria, Spain) to obtain
monthly optical (R-band) photo-polarimetric measurements of a sample of 34 of
the brightest gamma-ray, optical, and radio-millimeter blazars accessible from
the northern hemisphere.Comment: To be published in the proceedings of High Energy Phenomena in
Relativistic Outflows III (HEPRO III, IJMPCS). 4 page
Multi-wavelength variability study of the classical BL Lac object PKS 0735+178 on timescales ranging from decades to minutes
We present the results of our power spectral analysis for the BL Lac object
PKS 0735+178 utilizing the Fermi-LAT survey at high-energy -rays,
several ground-based optical telescopes, and single-dish radio telescopes
operating at GHz frequencies. The novelty of our approach is that, by combining
long-term and densely sampled intra-night light curves in the optical regime,
we were able to construct for the first time the optical power spectrum of the
blazar for a time domain extending from 23 years down to minutes. Our analysis
reveals that: (i) the optical variability is consistent with a pure red noise,
for which the power spectral density can well be approximated by a single
power-law throughout the entire time domain probed; (ii) the slope of power
spectral density at high-energy -rays (), is significantly
flatter than that found at radio and optical frequencies () within the
corresponding time variability range; (iii) for the derived power spectra we
did not detect any low-frequency flattening, nor do we see any evidence for
cut-offs at the highest frequencies down to the noise floor levels due to
measurement uncertainties. We interpret our findings in terms of a model where
the blazar variability is generated by the underlying single stochastic process
(at radio and optical frequencies), or a linear superposition of such processes
(in the -ray regime). Along with the detailed PSD analysis, we also
present the results of our extended (1998-2015) intra-night optical monitoring
program and newly acquired optical photo-polarimetric data for the source.Comment: The Astrophysical Journal, in pres
3 mm GMVA Observations of Total and Polarized Emission from Blazar and Radio Galaxy Core Regions
We present total and linearly polarized 3 mm Global mm-VLBI Array images of a
sample of blazars and radio galaxies from the VLBA-BU-BLAZAR 7 mm monitoring
program designed to probe the innermost regions of active galactic nuclei (AGN)
jets and locate the sites of gamma-ray emission observed by the Fermi-LAT. The
lower opacity at 3 mm and improved angular resolution, on the order of 50
microarcseconds, allow us to distinguish features in the jet not visible in the
7 mm VLBA data. We also compare two different methods used for the calibration
of instrumental polarisation and we analyze the resulting images for some of
the sources in the sample.Comment: Polarised Emission from Astrophysical Jets, June 12-16, 2017,
Ierapetra, Greec
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